![Industrial temperature transmitters Industrial temperature transmitters](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrTnJSmlNlTw5Hgi34Mn7LjstaEVvNaeAOE9a_XNBpatNntkDTUvfOG0r7lKwq4TTnPYmd9a1SswRcXifWHvowVosX7vpFJ3hcI8p2o0_VvqEFP99tM4TcsA6cClM-nTCORMuEoIIYH3U/s200/Temperature-Transmitters-Ives.jpg) |
Industrial temperature
transmitters (courtesy of
Siemens) |
Industrial temperature transmitters are devices that measure the temperature of a process and provide a measurable output over some desired temperature range. Industrial temperature transmitters primarily use either of two popular temperature sensors - the thermocouple or the RTD (resistance temperature detector). The RTD changes resistance as process temperature changes, while a thermocouple provides a changing micro-voltage with process temperature change. RTDs are inherently more accurate, but require excitation voltage. There are three style RTD's - 2-wire, 3-wire, and 4-wire.
Proper connections for all three types of RTD sensor to a user- configurable transmitter are shown in the following illustrations:
![proper wiring of RTDs proper wiring of RTDs](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEitKvRdVa00zBSwH1w5kWKxS0Q5VpX1r7hXsVGFH_0shBuoJf5AZASYqx5WsLMZzjmePnEEtGc9MsZ2yTGUtBEkglR5CIWY6g3_Zz_fGfiGHsc61RD5xXpv4p-uGiSYqvAxWrG2DolUKaA/s400/RTD-Connections.png) |
Proper wiring of RTDs |
It is critically important to note that the common connections shown by the symbols for 3- and 4-wire RTD sensors represent junction points at the sensor; not terminals jumpered by the technician at the time of installation, and not internal jumpers inside the transmitter. The whole purpose of having 3-wire and 4-wire RTD circuits is to eliminate errors due to voltage drop along the current-carrying wires, and this can only be realized if the “sensing” wire(s) extend out to the RTD itself and connect there. If the transmitter’s sensing terminal(s) are only jumpered to a current- carrying terminal, the transmitter will sense voltage dropped by the RTD plus voltage dropped by the current-carrying wire(s), leading to falsely high temperature indications.
Some of above content taken from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.